Disposable diapers have to a great extent replaced cloth diapers in the field of infant care. Many different styles of disposable diapers have been introduced to the marketplace, differing in materials, physical configuration, and cost.
One recurrent problem associated with the use of disposable diapers is the inability to quickly and conveniently determine when the diaper is wetted during use.
Various methods have been offered to provide wetness indicators in a disposable diaper. For example, U.S. Pat. No. 4,231,370 (Mroz et al) discusses the application of a flexible pH-change/color-change wetness indicator coating on the inwardly facing surface of a water-impervious thermoplastic backsheet of a disposable diaper. This approach has the disadvantage of requiring a separate coating material to be applied in an additional step. The preferred coating material itself is a complex four-component composition of two latex compositions, an acid buffer, and a pH-change/color-change material such as bromophenol blue. The mixing of these components is a long, complex process.
U.S. Pat. No. 4,611,576 (Colon) discloses a wetness-indicating hot-melt adhesive for a diaper. The adhesive composition includes water sensitive polymer and optional additional polymer resins; fatty acid with optionally an additional organic acid; optionally a water soluble wax; and a wetness indicating agent such as acid-base indicators. Like the '370 reference, this reference requires a complicated formulation to be prepared prior to production of the diaper. The adhesive product is applied to a substrate.
It is an object of the present invention to provide a thermoplastic film which is useful as a cover or backing sheet in a disposable diaper, and will change color when wet.